1. Field of the Invention
The present invention relates to a method of communication for transmitting digital information in time division multiplex frame to perform one-to-multiple digital communication, and in particular, to a method of communication, which is used in mobile wireless communication system such as personal handyphone system (PHS) or in local area network (LAN), in which modulation method can be selected.
The present invention also relates to a data transmission method and a data communication system for data transmission to transmit digital information on time division multiplex frame, and in particular, to a communication system, by which information can be transmitted at high speed when necessary.
2. Description of the Prior Art
As communication system for performing one-to-multiple digital communication, there are mobile wireless communication system such as portable telephone or wire communication system such as LAN. Description is given now on examples of conventional type communication method referring to FIG. 4 and FIGS. 11 to 13. As system configuration, there are one master device and a plurality of slave devices. A transmission frame in the direction to transmit from the master device to the slave device is called here a downward transmission frame, and a transmission frame in reverse direction is called an upward transmission frame. The upward and the downward frames use different carrier frequencies.
FIG. 4 shows a configuration of a transmission frame. The transmission frame is in 2.5 ms cycle in both upward and downward transmissions and comprises 4 time slots. Transmission capacity of one time slot is for 50 symbols in the downward frame and 40 symbols in the upward frame. Ten symbols of the upward transmission frame are for guide time to absorb propagation delay. Because QPSK (quadrature phase shift keying) capable to transmit 2 bits per symbol is used as modulation method in this transmission, transmission of 40 kb/s in downward transmission and 32 kb/s in upward transmission can be transmitted for one time slot.
FIG. 11 shows a configuration of a conventional type master device. Reference numeral 701 represents a data processing unit to exchange transmitting and receiving data and to allocate time slots. Reference numeral 702 represents a frame generating unit to assemble the downward frame using base band. Reference numeral 703 represents a QPSK modulator, and 704 a transmission antenna. Numeral 705 represents a receiving antenna, and 706 a QPSK demodulator. Numeral 707 represents a frame disassembling unit, which is in charge of frame synchronizing of the upward frame and divides the data to each time slot and delivers the data to the data processing unit 701.
FIG. 12 shows a configuration of a conventional type slave device. Reference numeral 801 represents a receiving antenna, and 802 represents a QPSK demodulator. Numeral 803 represents a frame disassembling unit, which is in charge of frame synchronizing of the downward frame and divides the data for each time slot and delivers the data to a data processing unit 804. The data processing unit 804 picks up only the data of time slot directed to it and outputs it, and further generates information for starting communication and inputs communication data and delivers the data to a time slot generator 805. The time slot generator 805 outputs a base band signal at time slot timing, at which transmission of the data from the data processing unit 804 is allowed. Reference numeral 806 represents a QPSK modulator, and 807 represents a transmitting antenna.
Next, description will be given on operation of this conventional example. FIG. 13 shows an outline of the operation. Communication is performed in two phases: a link setup phase and a communication phase. In the link setup phase, each of the master device and one slave device uses a time slot TS0 exclusively used for link setup and commonly possessed by the slave devices to request starting of communication or exchange information such as time slot numbers used in actual communication. In the subsequent communication phase, communication is performed with the time slot specified in the link setup phase. FIG. 13 shows an example where TS2 is specified. In the conventional communication method, communication is preformed in this manner.
FIG. 14 shows a configuration of a conventional type communication system. In FIG. 14, the conventional communication system comprises a center device 50 and a plurality of terminal devices 51 to 53.
FIG. 15 shows a configuration of a conventional type center device. The conventional type center device comprises a data processing unit 601 for exchanging data to be transmitted or received and for inputting or outputting data, control information, etc., a frame generating unit 602 for assembling a downward frame with base band according to the information from the data processing unit 601, a QPSK modulator 603, a transmitting antenna 604, a receiving antenna 605, a QPSK demodulator 606, and a frame disassembling unit 607 for performing frame synchronizing of an upward frame, picking up various types of information from the frame and delivering the data to the data processing unit 601.
FIG. 16 shows a configuration of a conventional type terminal device. The conventional type terminal device comprises a receiving antenna 901, a QPSK demodulator 902, a frame disassembling unit 903 for performing frame synchronizing of a downward frame, dividing various types of information in the frame, and delivering the data to the data processing unit 904, a data processing unit 904 for picking up and outputting only communication information directed to own station, generating an information to start communication, inputting communication data and delivering the data to a frame generating unit 905, a frame generating unit 905 for assembling an upward frame with base band according to the information from the data processing unit 904, a QPSK modulator 906, and a transmitting antenna 907.
In the following, description will be given on communication from the center device to the terminal devices 51 to 53, while description on communication in reverse direction is not given here because the same applies to the communication in reverse direction.
FIG. 17 shows a configuration of a data transmission method for transmitting data from the center device 50 to each of the terminal devices 51 to 53. In FIG. 17, the frame comprises a common unit 81, which contains a frame synchronizing pattern 82 and a control unit 83 and to be received by all terminal devices, and an information unit 84 to be received only by a specific terminal device. This frame is transmitted by xcfx80/4 shift QPSK.
Each of the terminal devices performs symbol synchronizing and frame synchronizing using the synchronizing pattern 82. Then, after having seen the content of the control unit 83, it is judged whether the information unit 84 is directed to itself or not. Accordingly, the center device can send information to any of the terminal devices if the terminal device to communicate is specified to the control unit 83.
However, the first-mentioned conventional communication method as described above is disadvantageous in that communication speed is constant, and it is not possible to provide transmission service at higher speed. To increase communication speed, it is necessary to change to a transmission mode at higher transmission speed, and all of the master device and the slave devices must be renewed. However, this requires much cost and results in waste of money because a slave device usable at lower transmitting speed also must be renewed to a device with higher transmitting speed.
In addition, in the second-mentioned conventional type data transmission method as described above, it is disadvantageous in that the speed of the information unit is constant and high-speed data transmission cannot be carried out. Also, to provide a new communication system for high-speed transmission, higher cost is required.
To solve the above first-mentioned problems of the conventional method, it is a first object of the present invention to provide a method of communication for providing high-speed transmission service by simply renewing only the master device and the slave devices, which are used for high-speed communication.
To solve the above second-mentioned problems, it is a second object of the present invention to provide a data transmission method and a data communication system, by which it is possible to transmit information at high speed when necessary.
To attain the first object, the communication method according to the present invention is characterized in that a modulation method to be used is specified in the link setup phase in addition to a free or empty time slot number and communication is carried out by this modulation method in the communication phase. If the modulation method is not specified, communication is carried out in the communication phase by the same modulation method as in the link setup phase.
Therefore, it is possible according to the present invention to provide transmission service at higher speed than in conventional system if a communication method capable to provide transmission at higher speed than the modulation method used in the link setup phase is specified in the communication phase because the slave devices not requiring high speed transmission can be used without any change, and no surplus cost is required.
To attain the above second object, according to the present invention, a modulation method of a communication information unit in the frame is turned to a modulation method having higher number of transmittable bits per unit time than the common unit when information is to be transmitted at high speed. Specifically, in case high-speed transmission is performed, the center device notifies the terminal device concerned that high-speed transmission is started from now on by the conventional modulation method using the communication information unit of the frame, and the terminal device to receive the frame demodulates the communication information unit depending upon the information using a demodulation unit corresponding the modulation method for high-speed transmission. As a result, it is possible to receive the information at higher speed.
In a conventional type terminal device not provided with the function to receive information at high speed, the common unit is transmitted by the conventional modulation method, and it is possible to maintain frame synchronizing and to receive the common unit. In this case, in the conventional type terminal device, the demodulation result of the communication information unit is indefinite in case of high-speed transmission, but there is no problem because no high-speed transmission is performed to the conventional type terminal device, which is not provided with a receiving means for receiving information at high speed.
The present invention provides a communication method for performing one-to-multiple digital communication between a master device and a plurality of slave devices, using a downward transmission frame to transmit from the master device to the slave device and an upward transmission frame to transmit from the slave device to the master device, at least one of the downward and upward transmission frames has a plurality of time slots, whereby, in a link setup phase at the start of communication, an information to specify time slot to be used in a communication phase is transmitted using one time slot each of the upward transmission frame and the downward transmission frame modulated by a first modulation method, and in case high-speed communication is performed, an information to specify a second modulation method to provide transmission at higher speed than the first modulation method is transmitted, and in case high-speed communication is not performed, an information to specify the same second modulation method as the first modulation method is transmitted, or the information to specify the second modulation method is not transmitted, and in the subsequent communication phase, communication is performed using the time slot specified in the link setup phase and by the second modulation method, and, in case there is no information to specify the second modulation method, communication is performed using the first modulation method, and a modulation method to provide high-speed communication can be selected.
The present invention also provides a communication method, wherein carrier frequency of a transmission frame using the second modulation method used in the communication phase is different from carrier frequency of the transmission frame used in the link setup phase, number of the time slots can be increased, and an exclusive carrier frequency can be used in the communication phase of high-speed transmission.
The present invention also provides a communication method, wherein multivalued number of modulation of the second modulation method is higher than the multivalued number of modulation of the first modulation method, and a multivalued modulation method at higher speed can be selected.
The present invention provides a communication method, wherein a symbol rate of the second modulation method is higher than a symbol rate of the first modulation method, and a modulation method with symbol rate of higher speed can be selected.
The present invention provides a master device for performing communication using the communication method, wherein said master device comprises a data processing unit for exchanging data to be transmitted or received and for allotting time slots, a frame generating unit for inputting transmission data from the data processing unit and for assembling a downward frame with base band, a plurality of modulators having different modulation methods, a first changeover switch for connecting the frame generating unit to one of a plurality of modulators, a transmission interface means leading to a transmission line, a second changeover switch for connecting the modulator connected to the first changeover switch of the transmission interface means, a receiving interface means for receiving data from the transmission line, a plurality of demodulators for demodulating signals with different modulating methods, a frame disassembling unit for performing frame synchronizing of the upward frame, dividing the data to each time slot and delivering the data to the data processing unit, and a third changeover switch for connecting one of a plurality of demodulators to the frame disassembling unit, whereby communication can be carried out by switching over to the modulators and the demodulators capable to perform high-speed communication.
The present invention provides a slave device for performing communication by the communication method, wherein the slave device comprises a data processing unit for picking up only data of the time slot directed to own station from received signal and for outputting the data, and for inputting transmission data and delivering the data to a time slot generator, a time slot generator for outputting a transmission data base band signal from the data processing unit to a time slot, in which transmission is allowed, a plurality of modulators having different modulation methods, a first changeover switch for connecting the time slot generator to one of a plurality of modulators, a transmission interface means for transmitting to a transmission line, a second changeover switch for connecting the modulator connected to the first changeover switch to the transmission interface means, a receiving interface means for receiving data from a transmission line, a plurality of demodulators for demodulating signals having different modulation methods, a frame disassembling unit for performing frame synchronizing of a downward frame, dividing the received data to each time slot and delivering the data to the data processing unit, and a third changeover switch for connecting one of a plurality of demodulators to the frame disassembling unit, whereby communication can be carried out by switching over to the modulators and the demodulators capable to provide high-speed communication.
The invention is characterized in that, in the communication of a center device and a plurality of terminal devices, data transmission from the center device to the terminal device is performed by a frame at a given cycle, the frame comprises a common unit to be received by all terminal devices and an individual unit to be received by a part of the terminal devices, the common unit is to be transmitted by a first modulation method and the individual unit is transmitted by a second modulation method having higher number of transmittable bits per unit than the first modulation method, and the invention has such an effect that information can be transmitted at higher speed than the conventional data transmission method.
The present invention provides a data transmission method, wherein the first modulation method is xcfx80/4 shift QPSK and the second modulation method is 16 QAM, and the invention has such an effect that information can be transmitted at higher speed than the conventional type data transmission method.
The present invention provides a data transmission method, wherein the first modulation method is xcfx80/4 shift QPSK and the second modulation method is 8 PSK, and the invention has such an effect that information can be transmitted at higher speed than the conventional type data transmission method as in the case of the invention according to the above.
The present invention provides a data transmission method, wherein a symbol rate of the second modulation method is made equal to a symbol rate of the first modulation method. By making the symbol rate of the second modulation method equal to that of the first modulation method, it is easier to maintain symbol synchronizing even in a conventional type terminal device and the required frequency range can be maintained as in the past.
The present invention provides a data transmission method, wherein the first modulation method is xcfx80/4 shift QPSK and the second modulation method is 16 QAM. In addition to the effect provided by the invention, it has such an effect that information can be transmitted at higher speed than the conventional data transmission method.
The present invention provides a data transmission method, wherein the first modulation method is xcfx80/4 shift QPSK and the second modulation method is 8 PSK. In addition to the effect provided by the invention, it has such an effect that information can be transmitted at higher speed than the conventional data transmission method.
The present invention provides a data communication system between a center device and a plurality of terminal devices, whereby the center device provides a frame at a given cycle, the frame comprises a common unit to be received by all terminal devices and an individual unit to be received by a part of the terminal devices so that the data can be transmitted from the center device to the terminal devices, the common unit is modulated by a first modulation method, the individual unit is modulated by a second modulation method having higher number of transmittable bits per unit time than the first modulation method, while, in a part of the terminal devices as described above, the common unit is demodulated by a first demodulation method corresponding to the first modulation method, and the individual unit is demodulated by a second demodulation method corresponding to the second modulation method. It has such an effect to transmit information at higher speed than the conventional data transmission method.
The present invention provides a center device in a data communication system between a center device and a plurality of terminal devices, whereby the center device at least comprises a frame forming means for forming a frame at a given cycle, the frame comprises a common unit to be received by all of the terminal devices and an individual unit to be received by a part of the terminal devices so that data can be transmitted from the center device to the terminal devices, a first modulation means for modulating the common unit by a first modulation method, and a second modulation means for modulating the individual unit by a second modulation method having higher number of transmittable bits per unit time than the first modulation method. By providing such a center device, the invention has an effect that information can be transmitted at higher speed than the conventional data transmission method.
The present invention provides a data communication system for performing data transmission from a center device to a plurality of terminal devices, the center device forms a frame at a given cycle, the frame comprises a common unit to be received by all terminal devices and an individual unit to be received by a part of the terminal devices at a given cycle, the common unit is modulated by a first modulation method, and the individual unit is modulated by a second modulation method having higher number of transmittable bits per unit time than the first modulation method, whereby a terminal device in a part of the terminal devices as described above at least comprises a first demodulation means for demodulating the common unit by a first demodulation method corresponding to the first modulation method, and a second demodulation means for demodulating the individual unit by a second demodulation method corresponding to the second modulation method. By providing such a terminal device, the invention has such an effect that information can be transmitted at higher speed than the conventional data transmission method.